DE 198 41 642 C2 discloses a high pressure fuel pump comprising a pump housing and several cylinder heads designed as cylinder inserts. Each cylinder insert is fixed in the pump housing via a spigot. An inlet line leads from the pump housing into the cylinder head. The fuel flows from the inlet line via an inlet valve into the cylinder chamber where it is compressed and finally flows, via a high pressure valve and a high pressure line, back to the pump housing, from where it flows to a common high pressure storage tank, the so-called common rail. An O-ring is arranged between the cylinder insert and the pump housing. The cylinder insert has a groove to accommodate the O-ring seal. The insertion of the O-ring requires a high assembly cost and it is easily possible for the O-ring to be positioned wrongly in the groove. When the cylinder insert is screwed in place, the O-ring is squashed between the sealing faces of the two components and is thus damaged, thereby allowing fuel to flow out of the high pressure fuel pumps.